我在做什么错..Android编程新手

Question

我正在尝试在Android中创建自定义ListView ArrayAdapter，以显示来自我创建的名为Brick的类的数据。 我的主要活动是调用一个返回ArrayList的方法。 我不知道自己在做什么错，LogCat和Debugger并没有告诉我太多。 我认为这是我的错误，因为它是Android的新手。 当我启动ListActivity时，应用程序强制关闭。 我已经尝试了多个教程，但进展很快。

这是我的自定义适配器：

import android.view.View;
import android.view.ViewGroup;
import android.widget.ArrayAdapter;
import android.widget.TextView;

public class BrickListAdapter extends ArrayAdapter<Brick> {

private ArrayList<Brick> bricks;
private Context mContext;
public BrickListAdapter(Context context, int textViewResourceId, ArrayList<Brick> objects) {


    super(context, textViewResourceId, objects);
    // TODO Auto-generated constructor stub
    this.bricks = objects;
    this.mContext = context;
}

@Override
public View getView(int position, View convertView, ViewGroup parent) {
View v = convertView;

if(v != null){
    LayoutInflater vi = (LayoutInflater)mContext.getSystemService(Context.LAYOUT_INFLATER_SERVICE);
    v = vi.inflate(R.layout.bricklistitems, null);

    Brick b = bricks.get(position);

    if(b != null){
        TextView tn = (TextView) v.findViewById(R.id.listitemname);
        TextView td = (TextView) v.findViewById(R.id.listitemdesc);

        if(tn !=null){
            tn.setText(b.getName());
        }
        if(td != null){
            td.setText(b.getWidth());
        }

    }
    }

return v;
}



}

这是我的ListActivity：

  public class ListActivity extends Activity {


private static  ArrayList<Brick> a;
@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_list);

     a = new BrickTypes().getBrickTypes();






    BrickListAdapter adapter = new BrickListAdapter(this, R.layout.bricklistitems, a);

    ListView lv = (ListView) findViewById(R.id.listView1);

    lv.setAdapter(adapter);

}

@Override
public boolean onCreateOptionsMenu(Menu menu) {
    // Inflate the menu; this adds items to the action bar if it is present.
    getMenuInflater().inflate(R.menu.list, menu);
    return true;
}





 }

好的，这是LogCat。 我看到我收到了NullPointerException，但我不明白是什么。

10-31 03:55:22.772: E/AndroidRuntime(4799): FATAL EXCEPTION: main
10-31 03:55:22.772: E/AndroidRuntime(4799): java.lang.NullPointerException
10-31 03:55:22.772: E/AndroidRuntime(4799): at android.widget.AbsListView.obtainView(AbsListView.java:2269)
10-31 03:55:22.772: E/AndroidRuntime(4799): at android.widget.ListView.measureHeightOfChildren(ListView.java:1244)
10-31 03:55:22.772: E/AndroidRuntime(4799): at android.widget.ListView.onMeasure(ListView.java:1156)
10-31 03:55:22.772: E/AndroidRuntime(4799): at android.view.View.measure(View.java:15172)
10-31 03:55:22.772: E/AndroidRuntime(4799): at android.widget.RelativeLayout.measureChild(RelativeLayout.java:602)
10-31 03:55:22.772: E/AndroidRuntime(4799): at android.widget.RelativeLayout.onMeasure(RelativeLayout.java:415)
10-31 03:55:22.772: E/AndroidRuntime(4799): at android.view.View.measure(View.java:15172)
10-31 03:55:22.772: E/AndroidRuntime(4799): at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:4814)
10-31 03:55:22.772: E/AndroidRuntime(4799): at android.widget.FrameLayout.onMeasure(FrameLayout.java:310)
10-31 03:55:22.772: E/AndroidRuntime(4799): at android.view.View.measure(View.java:15172)
10-31 03:55:22.772: E/AndroidRuntime(4799): at android.widget.LinearLayout.measureVertical(LinearLayout.java:833)
10-31 03:55:22.772: E/AndroidRuntime(4799): at android.widget.LinearLayout.onMeasure(LinearLayout.java:574)
10-31 03:55:22.772: E/AndroidRuntime(4799): at android.view.View.measure(View.java:15172)
10-31 03:55:22.772: E/AndroidRuntime(4799): at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:4814)
10-31 03:55:22.772: E/AndroidRuntime(4799): at android.widget.FrameLayout.onMeasure(FrameLayout.java:310)
10-31 03:55:22.772: E/AndroidRuntime(4799): at com.android.internal.policy.impl.PhoneWindow$DecorView.onMeasure(PhoneWindow.java:2148)
10-31 03:55:22.772: E/AndroidRuntime(4799): at android.view.View.measure(View.java:15172)
10-31 03:55:22.772: E/AndroidRuntime(4799): at android.view.ViewRootImpl.performMeasure(ViewRootImpl.java:1848)
10-31 03:55:22.772: E/AndroidRuntime(4799): at android.view.ViewRootImpl.measureHierarchy(ViewRootImpl.java:1100)
10-31 03:55:22.772: E/AndroidRuntime(4799): at android.view.ViewRootImpl.performTraversals(ViewRootImpl.java:1273)
10-31 03:55:22.772: E/AndroidRuntime(4799): at android.view.ViewRootImpl.doTraversal(ViewRootImpl.java:998)
10-31 03:55:22.772: E/AndroidRuntime(4799): at android.view.ViewRootImpl$TraversalRunnable.run(ViewRootImpl.java:4212)
10-31 03:55:22.772: E/AndroidRuntime(4799): at android.view.Choreographer$CallbackRecord.run(Choreographer.java:725)
10-31 03:55:22.772: E/AndroidRuntime(4799): at android.view.Choreographer.doCallbacks(Choreographer.java:555)
10-31 03:55:22.772: E/AndroidRuntime(4799): at android.view.Choreographer.doFrame(Choreographer.java:525)
10-31 03:55:22.772: E/AndroidRuntime(4799): at android.view.Choreographer$FrameDisplayEventReceiver.run(Choreographer.java:711)
10-31 03:55:22.772: E/AndroidRuntime(4799): at android.os.Handler.handleCallback(Handler.java:615)
10-31 03:55:22.772: E/AndroidRuntime(4799): at android.os.Handler.dispatchMessage(Handler.java:92)
10-31 03:55:22.772: E/AndroidRuntime(4799): at android.os.Looper.loop(Looper.java:137)
10-31 03:55:22.772: E/AndroidRuntime(4799): at android.app.ActivityThread.main(ActivityThread.java:4745)
10-31 03:55:22.772: E/AndroidRuntime(4799): at java.lang.reflect.Method.invokeNative(Native Method)
10-31 03:55:22.772: E/AndroidRuntime(4799): at java.lang.reflect.Method.invoke(Method.java:511)
10-31 03:55:22.772: E/AndroidRuntime(4799): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:786)
10-31 03:55:22.772: E/AndroidRuntime(4799): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:553)
10-31 03:55:22.772: E/AndroidRuntime(4799): at dalvik.system.NativeStart.main(Native Method)
10-31 03:55:22.801: W/ActivityManager(157):   Force finishing activity net.stewartservices.brickconverter/.ListActivity

Answer 1

更改getView()方法

@Override
public View getView(int position, View convertView, ViewGroup parent) {
View v = convertView;

if(v == null){// Changed Here
    LayoutInflater vi = (LayoutInflater)mContext.getSystemService(Context.LAYOUT_INFLATER_SERVICE);
    v = vi.inflate(R.layout.bricklistitems, null);
      }

        Brick b = bricks.get(position);   
        TextView tn = (TextView) v.findViewById(R.id.listitemname);
        TextView td = (TextView) v.findViewById(R.id.listitemdesc);

        if(tn !=null){
            tn.setText(b.getName());
        }
        if(td != null){
            td.setText(""+ b.getWidth());// Changed Here
        }

return v;
}

Answer 2

这可能是导致错误的原因：

td.setText(b.getWidth());

这可能是调用带有资源ID的setText（）。 请改用此代码（采用CharSequence的代码）：

td.setText("" + b.getWidth());